Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $228.97   6.727%   $244.3728   $244.37   $244.35   $244.40  
  Purchase #2 $172.69   11.388%   $192.3559   $192.36   $192.35   $192.40  
  Purchase #3 $192.66   10.582%   $213.0473   $213.05   $213.05   $213.00  
  Purchase #4 $54.86   11.163%   $60.984   $60.98   $61.00   $61.00  
  Purchase #5 $201.63   5.445%   $212.6088   $212.61   $212.60   $212.60  
  Purchase #6 $54.40   13.296%   $61.633   $61.63   $61.65   $61.60  
  Purchase #7 $197.90   11.471%   $220.6011   $220.60   $220.60   $220.60  
  7 purchase totals = $1,103.11       $1,205.6029   $1,205.60   $1,205.60   $1,205.60